Wildfire is a natural process that plays an important role in forest ecosystems, but many wildfires are caused by human activity. These include fireworks, runaway campfires, improperly extinguished cigarettes, and chainsaw use in areas with a lot of brush or dead trees. Wind can also cause wildfires by spreading the flames or blowing them across the landscape.
The severity of wildfires depends on the amount and type of combustible material present, the physical setting (e.g., topography), and the weather conditions. Drought and heat increase the risk of fire by drying out fuels, making them more likely to ignite. The presence of heavy limbs, stumps, and organic debris in the landscape increases the intensity of fire, because they take longer to burn than light fuels like leaves, grasses, or shrubs.
During the past few decades, the number of acres burned by wildfires in the United States has increased significantly. This has largely been due to climate change, as well as the historic practice of putting out all fires, which has led to an unnatural buildup of fuel and left ecosystems more susceptible to flames.
Wildfires can have devastating impacts on human communities. Direct costs are high and can include the destruction of structures, loss of income and livelihoods, and health-related issues. Exposure to biomass smoke can lead to respiratory morbidity and mortality, with links to cardiovascular, ophthalmic, and psychiatric disorders. Some populations, particularly in the wildland-urban interface, are at especially high risk of impact.